The most widely used on-site wastewater treatment systems for individual households have traditionally been either septic systems or aerobic treatment units. Septic systems generally include a septic tank followed by a leaching tile field or a similar absorption device located downstream, but physically on-site of the individual residence. The septic tank allows for larger/heavier solids in the sewage to settle out within the tank, while anaerobic bacteria partially degrade the organic material in the waste. The discharge from the septic tank is further treated by dispersion into the soil through any number of soil absorption devices, such as a leaching tile field, whereby bacteria in the soil continue the biodegradation process.
The conventional septic system is typically a flow-through system. The septic tank and the tile field are positioned so that sewage is carried out of the residence and through the treatment system by gravity and hydraulic displacement. As a flow-through system, the tank relies on sufficient hydraulic capacity to slow the velocity of the flow and allows settling of the solids to take place. Unfortunately, as the settable solids accumulate in the bottom of the tank, they displace the beneficial tank volume, effectively increasing the velocity of flow through the tank and decreasing the efficiency of solids removal. Also, as a flow-through system, the velocity of the flow through the tank and the related efficiency of solids removal by gravity are dependent upon the volume and frequency of the incoming sewage. A lower volume and rate of incoming sewage flow allows for greater gravity separation and removal efficiency. Higher volumes and rates of flow therefore decrease gravity settling and solids removal efficiency. Over the course of time, an increasing in volume of organic material is discharged from the tank (due to decreasing removal efficiency) until the total volume of solids discharged over the life of the system exceeds the capacity of the downstream soil absorption system (leaching tile field) to accomplish further treatment. The soil absorption system will then retain solids and become plugged, thereby causing a back-up of sewage into the home. In this situation, the downstream soil absorption system is considered failed. Rejuvenation of a failed soil absorption system is not technologically feasible. Therefore, the downstream soil absorption system or other downstream device must be replaced or a new downstream device installed. However, even if sufficient land area is available toward the installation of a new downstream device, such can be accomplished only at considerable cost and inconvenience. Typically, heavy construction equipment is required to excavate and install any new replacement leaching tile field (a commonly used soil absorption system), or a similar device. This is much more inconvenient and costly then at the time of installation of the original treatment system. Construction equipment operating around an occupied residence frequently requires considerable destruction of hundreds of square feet of existing sod or lawn, moving fences, trees or recreational equipment, and creating a hazard for individuals, particularly smaller children.
Most aerobic treatment units are also flow through systems. Unlike septic tanks, aerobic treatment units perform primary (anaerobic) treatment and secondary (aerobic) treatment within the confines of the system. This arrangement provides a much higher degree of treatment within a relatively small area. As traditional aerobic treatment units are designed for a much higher removal of solids and organic compounds than anaerobic treatment units, a downstream device is frequently not required or is severely diminished in size compared to one which would be required downstream of a septic tank. In a traditional aerobic treatment unit, the first stage of the process is called pretreatment and provides for anaerobic treatment very much like that provided by a septic tank. A separate, isolated pretreatment chamber contains sufficient hydraulic capacity to slow the velocity of the flow somewhat and allows the settling of some of the solids to take place. Anaerobic bacteria partially degrade the organic material in the waste. As a flow through system, the contents of the pretreatment chamber (partially treated waste) are displaced by incoming sewage, and are transferred to the aeration chamber or biological reactor.
Within the aeration chamber, air is introduced in controlled amounts creating a proper environment for the development of a number of types of aerobic bacteria. The aerobic bacteria maintain a higher metabolic rate than anaerobic bacteria, which causes them to readily consume the organic material contained in the pretreated sewage. Prior to discharge of this flow through system, the aerobic bacteria (commonly called activated sludge) must be separated from the treated liquid. If the activated sludge particles are allowed to exit the system, two problems occur. First, the activated sludge would not be available to treat additional incoming sewage. As the system is operated on a continuing basis, the cultured bacteria need to be retained for future use. Secondly, if the activated sludge is allowed to be discharged from the system, the organic nature of the sludge would be considered a pollutant if returned directly to the environment.
Commonly, the activated sludge is separated from the treated liquid by allowing the solids to settle out in a gravity clarifier. In a flow through system, the contents of the aeration chamber containing the activated sludge are hydraulically displaced to the clarifier by partially treated liquid entering from the pretreatment chamber. Once in the gravity clarifier, quiescent conditions allow the activated sludge to slowly settle to the bottom of the chamber while the treated liquid is discharged from the system near the top of the chamber. The clarifier relies on having sufficient hydraulic capacity to slow the velocity of the flow through the chamber and thereby allows the activated sludge solids to settle to the bottom. The settled sludge at the bottom of the clarifier is returned, by various means, to the aeration chamber. This return prohibits the clarifier from accumulating a large volume of solids and thereby reducing the efficiency of solids separation. However, as a flow through system, the settling efficiency of the clarifier is dependent also on the volume and frequency of the incoming sewage flow.
From the foregoing, it is clearly seen that the efficient and long-term operation of a flow through septic system or a flow through aerobic treatment unit is dependent on eliminating surges and maintaining a uniform, consistent rate of flow through the system. Unfortunately, a uniform, consistent rate of flow through a residential wastewater system is not commonly achieved. Modern homes are furnished with many water using appliances that generate large volumes of sewage flow in compressed periods of time. Wastewater from washing machines, dishwashers, hot tubs, spas, and similar appliances tend to be high in volume and discharge within a short period of time. These concentrated hydraulic surges disrupt the quiescent environment of septic tanks or aerobic treatment units, reducing efficiency of the gravity settling process. This effect causes partially treated waste or biological solids to be discharged to a downstream soil absorption system or other downstream treatment device resulting in premature failure, or causes biological solids to be returned to the environment as a pollutant.
An object of the present invention is to enhance the operation of new or existing septic tanks or aerobic treatment units to prohibit the discharge of partially treated waste or other organic solids. By installing a novel wastewater treatment unit of the present invention downstream of a new or existing septic tank or an aerobic treatment unit, but upstream of a soil absorption system, device or a discharge point, the discharge of partially treated waste or other organic solids is substantially totally precluded. In particular, the wastewater treatment unit of the present invention is of a relatively compact size and its installation as aforesaid can be accomplished with minimum disturbance to existing yards, landscaping or home sites whose downstream soil absorption system is being newly installed or has been installed for a time and is failing. Even if the downstream treatment system has not failed, the installation of the wastewater treatment unit of the present invention provides enhanced performance benefits to new or previously installed residential wastewater treatment systems at a minimum of cost, effort and installation time. By thus installing the wastewater treatment unit of the present invention into or as part of a residential wastewater treatment system, an increase in the serviceability of the latter is automatically achieved. As the total volume of solids discharged by a secondary treatment system typically accumulate in the downstream soil absorption system or device, premature failure is common. Removal of accumulated solids from a failed or plugged soil absorption device is not technological feasible, but rejuvenation thereof can be achieved by the present invention in the sense that the wastewater treatment unit of the present invention can be installed upstream from the failed soil absorption system and will accumulate solids which can in turn be removed readily from grade thereby preventing solids from passing beyond the wastewater treatment unit to the failed soil absorption system. In this fashion the wastewater treatment unit of the present invention can rejuvenate wastewater treatment systems which have failed and, if installed prior to such failure, can extend the life thereof.
The latter objects are achieved by a novel wastewater treatment unit utilizing substantially the wastewater treatment mechanism disclosed in U.S. Pat. No. 5,264,120 granted on Nov. 23, 1993 which is housed in a settling and retention basin which collects solids from domestic wastewater discharge. The settling and retention basin includes an inlet and an outlet pipe or invert which are respectively connected to the discharge of a flow-through septic system or a flow-through aerobic treatment unit and a soil absorption system (leaching tile field) or any such other downstream treatment device. Wastewater enters the settling and retention basin and before being discharged therefrom passes through and is treated by a wastewater treatment mechanism (similar to that of U.S. Pat. No. 5,264,120 which is known in the trade as assignee""s Bio-Kinetic(copyright) device) which contains three filtration zones, eight settling zones, 37 baffled chamber plates and 280 lineal feet of kinetic filtration, all of which dramatically reduce loading on downstream soil absorption systems. Moreover, within the Bio-Kinetic(copyright) device are settling zones which operate in conjunction with filtration and flow equalization to effectively retain BOD and solids which are removed from the flow stream. The Bio-Kinetic(copyright) device includes flow equalization ports arranged to manage daily flow variations and control flow through all upstream and downstream treatment processes, higher sustained flow ports which become operative under longer hydraulic surges and, finally, peak flow ports which operate under high, prolonged flow surges. Thus, under all three potential flow patterns, the solids can be settled by the Bio-Kinetic(copyright) device and retained in the settling and retention basin for subsequent removal from grade. Since the settling and retention basin has a normal capacity of 52 gallons below an outlet invert, normal liquid and solids retention capacity is quite high, but for special applications additional ring sections and riser sections can be added to dramatically increase the volume of the retention basin and allow water-tight installation at burial depths of up to 12 feet. However, an upper end of the settling and retention basin is at all times exposed above grade and is closed by a heavy duty access cover which permits the removal and cleaning of the Bio-Kinetic(copyright) device, the removal of solids from the settling and retention basin, and the re-installation of the Bio-Kinetic(copyright) device into the settling and retention basin for continued use. Thus, by installing the wastewater treatment unit of the present invention upstream of new or existing tile fields, sand filters, leaching fields, mounds, irrigation systems, constructed wet lands or any process that is biologically sensitive, hydraulically sensitive or difficult to replace, effective wastewater treatment is assured through the settling and storage of suspended solids, flow equalization, filtration and, if desired, chemical addition.
Thus, upon the installation of the wastewater treatment unit of the present invention immediately downstream of a new or existing septic tank or an aerobic treatment unit, the following advantages are achieved:
a) direct filtration and settling of treated wastewater or treated effluent,
b) beneficial flow equalization through all upstream and downstream treatment stages,
c) the addition of downstream chemicals via chemical feeders,
d) the enhancement of beneficial nitrification, and
e) the enhancement of beneficial de-nitrification.
With the above and other objects in view that will hereinafter appear, the nature of the invention will be more clearly understood by reference to the following detailed description, the appended claims and the several views illustrated in the accompanying drawings.